1. Field of the Invention
The present invention generally relates to an electric rotating machine. More particularly, the present invention relates to an electric rotating machine such as a starter motor for vehicles that can suitably be used as an electric motor for high-speed rotations.
2. Related Art
Japanese Unexamined Patent Publication No. 2-241346, which corresponds to U.S. Pat. No. 5,130,596, discloses an electric rotating machine having upper and lower armature coils held within slots of an armature core. The coils are extended in the axial direction to be cylindrical, with the outer periphery of the upper coil being smaller in diameter than the outer periphery of the armature core. The metal brush contacts the outer periphery of the cylindrical surface. In this arrangement, the upper and lower armature coils are fed with electric current through the metal brush.
However, such an electric motor, particularly when used for high-speed rotation, has the problem that high-speed rotation is disabled by heavy mechanical loads caused by burdens on the molded resin cylinder, which holds the coils composing the contact face for the metal brush. The burdens on the molded resin cylinder are due to the centrifugal force developed on the commutator face of the coil, heavy thermal loads caused by the effect of the resisting heat generated on the commutator face, and the frictional heat generated on the metal brush in high-speed rotations.